Interferometric measuring devices for determination of length are known which are suitable for study of samples that are of sufficient dimensions.
But these known devices are poorly adapted to the measurement of small samples with a low coefficient of dilatation, as in the case when a material is received for the first time, for example material obtained by crystal growth, in very small dimensions. It is important in numerous cases to be able to determine with good precision the coefficient of thermal dilatation of this new material, to decide if it is suitable for the purpose that is sought before engaging large amounts of money to get larger samples.
The invention is intended to remedy these drawbacks, with development of a device that can be rapidly and readily adapted to samples of different sizes, and that assures rapid placement and precise positioning of the sample that is to be measured.
According to the invention, an interferometric device for measurement of variations in length of a sample under the influence of temperature, said length being between a plane of reference and a measurement plane defined by the two plane terminal faces of the sample, comprising a source of monochromatic light, means to form parallel beams from said source, a thermostatic enclosure, means to vary the temperature in the enclosure, a sample holder disposed in the enclosure, a reference reflecting surface, a measuring reflecting surface connected to the measurement plane, means to cause the two beams reflected respectively by the two reflecting surfaces to interfere, and a sensor to observe and measure interference fringes, is improved in that the reference reflecting surface is disposed inside the thermostatic enclosure, and in that the sample holder presents a bearing surface for the terminal reference face of the sample, elastic means are provided to apply the sample against said bearing surface, and a support is provided for the reference reflecting surface, so designed that the variation of distance between the two reflecting surfaces is constantly equal to the variation in length of the sample when the temperature of the thermostatic enclosure is modified.
Other features of the invention will become evident from the detailed description that is to follow.